Bleaching method



BLEACHING METHOD Julien Dungler, Basel, Switzerland N Drawing. Application May 23, 1955 Serial No. 510,501

Claims priority, application France June 1, 1954 9 Claims. (Cl. 8-108) The present invention relates to chemical bleaching processes adapted for bleaching most various materials, such as natural, artificial or synthetic fibres mainly of cotton, fiax, hemp, jute, nylon, perlon, or others, paper, etc., by destroying the coloring matter through oxidation, the bleaching effect being obtained by virtue of a reaction between an acid and a bleaching agent, generally a chlorine compound, under the action of heat.

Such a bleaching treatment is often carried out on a product to be bleached such as, for instance, a fabric which has just been subjected to another previous treatment, such as size removing, scalding or other treatment, so that it is impregnated with a treating agent, the presence of which in the fabric necessitates a preliminary treatment before it is possible for the product to be subjccted to the bleaching treatment.

In the case, for instance, of a fabric which has just been freed of its size and scalded by means of caustic soda the bleaching of this fabric, at the present time, is carried out in the following manner: the caustic soda which impregnates the fabric is first neutralized by means of sulphuric acid (H 50 with an excess of acid ensuring the complete neutralization of the caustic soda. This excess of acid is then neutralized, in its turn, with sodium carbonate. The fabric is then soaped and rinsed until it becomes neutral (pH=7).

The bleaching operation is then effected, for instance by means of chloride, by introducing the fabric into a bath containing chlorite and an acid such as formic acid. After being impregnated, the fabric is squeezed and introduced into a treating chamber where it is exposed to heat which brings about a reaction between the chlorite and the acid, leading to the formation of chlorine dioxide constituting finally the oxidising agent which ensures the bleaching effect. It is further to be noted that this reaction must be controlled in such manner as to prevent the formation of chlorate which attacks the fibres, a condition which is very difficult to attain even by providing an excess of acid.

The main object of the present invention is to considerably simplify the chemical bleaching treatment while reducing the amounts of the reagents involved.

To this end, the bleaching process according to the invention consists in first impregnating throughout, i. e. from its surface to its very core, the material to be bleached with an acid, then impregnating said material over its surface with a bleaching agent such as a chlorine compound, and then exposing to heat the material thus impregnated to the core thereof with an acid and over its surface with a bleaching medium.

When the material to be bleached has just been subjected to a preliminary treatment such as size removing, scalding or other treatment, effected by means of a basic reagent which must be neutralized by an acid prior to the beginning of the bleaching treatment, according to another feature of the invention, the material to be bleached and impregnated with the basic reagent is introduced into a neutralizing bath containing an excess of acid beyond the amount which is necessary for the desired neutralization and sufficient for affording the desired acid impregnation to the core, the material to be bleached being then impregnated over its surface with a bleaching agent and then exposed to heat.

According to another feature of the invention, the acid impregnation to the very core of the material is ensured by passing the material through a bath constituted by a weak acid, such as formic acid, phosphoric acid or the like, and maintained up to its boiling temperature or a temperature near the latter.

According to another feature of the invention, the superficial impregnation with a bleaching agent is effected by having the treated material previously impregnated to the core thereof with an acid passed through a bath constituted by water containing, preferably, per liter, 5 to 30 grams of bleaching agent such as chlorine, hypochlorite or other chlorine compound, according to the state of the product to be bleached.

According to another feature of the invention, the material to be bleached is squeezed down until it contains about 70% of liquid based on its weight when dry, after having passed through a bath for being acidified to the core.

According to another feature of the invention, the product to be bleached is squeezed down until it contains about to of liquid based on its weight when dry, after its passage through the bleaching bath.

Other and further objects and advantages of the invention will be apparent to those skilled in the art from a consideration of the following description of the process according to the invention as applied to the bleaching operation of a cotton fabric which has just been subjected to a scalding by means of caustic soda.

As usual, the scalded fabric impregnated with caustic soda is caused to pass through an acid bath adapted to neutralize said caustic soda. However, in contradistinction with the known methods, this neutralization is not effected by means of a strong acid such as sulphuric acid, but, in view of the subsequent bleaching operation, by means of a weak acid, such as formic acid, phosphoric acid or other acid. Thus, the bath may contain for example 20 cubic centimeters of formic acid per liter.

In order to obtain the effect sought for with this weak acid, the bath is brought, according to another feature of the invention, up to its boiling temperature or a temperature near the latter, which yields to the reaction the necessary strength. When coming into contact with this nearly boiling acid, the caustic soda is instantaneously neutralized and soda formate is formed. It is further to be noted that the bath is controlled in such a manner that there always remains an excess of acid subsequent to the neutralization of the caustic soda.

In this manner, the fabric is impregnated to its very core with formic acid at the exit of the bath. It is then squeezed down until it contains about 70% of liquid based on its weight when dry and introduced into a bath containing the bleaching agent.

This bath is constituted, for instance, by Water containing, per liter, 5 to 30 grams of a bleaching agent such as soda chlorite, hypochlorite or other chlorine compounds, according to the state of the fabric, for instance according to the importance of the motes." This bath need not be heated. Furthermore, it may comprise an addition of formic acid, but this is not at all necessary.

Since the fabric reaching into this bath of a bleaching agent is already impregnated to the core thereof with formic acid, the impregnation with the bleaching agent is effected substantially over the surface thereof only.

3 This prevents the formation of chlorate and, furthermore, permits the use of a smaller amount of bleaching agent, since this superficial impregnation absorbs but a very small amount of the latter, in contradistinction with the known methods, where the fabric is impregnated to the core thereof with a bath containing at the same time the chlorite and an acid.

At the exit of the bath, the fabric is squeezed down until it contains about 90 to 100% of liquid based on its weight when dry and introduced into a treating chamber where it is exposed to the action of heat. The chlorine dioxide formed by the reaction between the formic acid and the chlorite, or other chlorine compound, then brings about the desired destruction of the coloring material by oxidation thereof.

It is to be noted that, in the method according to the invention as hereinabove described, the same acid, namely the formic acid in the example contemplated, acts, first to neutralize the caustic soda and, second insures the formation of the chlorine dioxide, from chlorite.

Therefore, it is unnecessary to provide for the operations intended for neutralizing the acid used for the neutralization of the caustic soda and also for the soaping and rinsing operations which were necessary in the known methods. Furthermore, as already hereinabove set forth, the method makes it possible to use less bleaching agent since the latter does not practically penetrate to the core of the material to be bleached. This mere superficial impregnation also prevents the formation of chlorate.

In the case of fabrics made of rayon or rayon staple, the size removing and the scalding operations are effected by means of a mixture of soda carbonate, of trisodium phosphate bleaching liquid (Javel water) and a wetting agent. The fabric impregnated with this mixture is passed into a bath of formic acid brought up to a temperature at least near the boiling temperature. Then the process is continued as in the preceding example. Bleaching liquid (Javel water) may also be used as a bleaching agent instead of the chlorite.

In the case of paper or cellulose forming a paste in the shape of a thin sheet, the material is introduced into the bath with formic acid which then may be used under cold conditions since this acid needs no longer ensure the neutralization of an agent remaining as a consequence of a previous treatment. However, there are obtained the advantages of the method according to the invention resulting from the impregnation of the material to the core thereof with acid followed by a surface impregnation with a bleaching agent.

The method may also be applied to a substance, cellulose or other, in a fiocky state. In this case, the impregnation with acid is not effected in a bath but in any other suitable manner, for example inside a vat filled up with the flocky material, and into which the acid is poured in order to impregnate the fiocky material to the core thereof prior to its superficial impregnation with a bleaching agent.

As many changes could be made in the above process without departing from the scope of the claims, it is in tended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. In a process of bleaching organic fibrous material wherein the material while in contact with both a chlorine compound selected from the group consisting of a chlorite and a hypochlorite bleaching agent and an acid is subjected to heat to cause a reaction between the chlorine compound and acid to bleach the fibrous material, the steps which comprise thoroughly impregnating the fibrous material to the core thereof with the acid, removing excess acid from the material by s --i-ng same, thereafter contacting the material While tfioroughly impregnated to the core thereof with acid with a solution containing the chlorine compound to impregnate substantially only the surface of the material with the chlorine compound, removing excess chlorine compound from the material by squeezing same, and subjecting the impregnated material to sufficient heat to cause the acid and the chlorine compound in the material to react and cause a bleaching of the material.

2. A process as recited in claim 1 wherein the acid is formic acid.

3. A process as recited in claim 1 wherein the acid is phosphoric acid.

4. A process as recited in claim 1 wherein the fibrous material is impregnated with an alkali prior to impregnation with the acid and sufiicient acid is used in the acid impregnation step to neutralize said alkali and thoroughly impregnate the material to the core with the acid.

5. A process as recited in claim 1 wherein the chlorine compound is a chlorite.

6. A process as recited in claim 1 wherein the chlorine compound is a hypochlorite.

7. A process as recited in claim 1 wherein the fibrous material after impregnation with the acid is squeezed until it contains about of liquid based on the dry weight of the material.

8. A process as recited in claim 1 wherein the fibrous material after impregnation with the chlorine compound is squeezed until it contains about to of liquid based on the dry weight of the material.

9. In the process of bleaching organic fibrous material wherein the material while in contact with both a chlorine compound selected from the group consisting of a chlorite and a hypochlorite bleaching agent and an acid is subjected to heat to cause a reaction between the chlorine compound and the acid to bleach the material, the steps which comprise immersing the material in a bath of said acid to thoroughly impregnate the material to the core thereof, removing the material from the bath and removing excess acid therefrom, immersing the material thus impregnated to the core thereof with the acid in a second bath containing the chlorine compound in solution to impregnate substantially only the surface of the material with the chlorine compound, removing the material from the second bath, removing excess chlorine compound from the material and subjecting the material to sufficient heat to cause the chlorine compound and the acid to react to cause a bleaching of the material.

References Cited in the file of this patent UNITED STATES PATENTS 73,733 Luther Jan. 28, 1868 2,377,171 Murdock May 29, 1945 2,521,340 Carr Sept. 5, 1950 2,526,839 Aston Oct. 24, 1950 FOREIGN PATENTS 552,711 Great Britain Apr. 21, 1943 567,774 Great Britain Mar. 2, 1945 473,980 Canada May 29, 1951 

1. IN A PROCESS OF BLEACHING ORGANIC FIBROUS MATERIAL WHEREIN THE MATERIAL WHILE IN CONTACT WITH BOTH A CHLORINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF A CHLORIDE AND A HYPOCHLORITE BLEACHING AGENT AND AN ACID IS SUBJECTED TO HEAT TO CAUSE A REACTION BETWEEN THE CHLORINE COMPOUND AND ACID TO BLEACH THE FIBROUS MATERIAL, THE STEPS WHICH COMPRISE THROUGHLY IMPREGNATING THE FIBROUS MATERIAL TO THE CORE THEREOF WITH THE ACID, REMOVING EXCESS ACID FROM THE MATERIAL BY SQUEEZING SAME, THEREAFTER CONTACTING THE MATERIAL WHILE THROUGHLY IMPREGNATED TO THE CORE THEREOF WITH ACID WITH A SOLUTION CONTAINING THE CHLORINE COMPOUND TO IMPREGNATE SUBSTANTIALLY ONLY THE SURFACE OF THE MATERIAL WITH THE CHLORINE COMPOUND, REMOVING EXCESS CHLORINE COMPOUND FROM THE MATERIAL BY SQUEEZING SAME, AND SUBJECTING THE IMPREGNATED MATERIAL TO SUFFICIENT HEAT TO CAUSE THE ACID AND THE CHLORINE COMPOUND IN THE MATERIAL TO REACT AND CAUSE A BLEACHING OF THE MATERIAL. 